Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$165.57	6.483%	$176.3039	$176.30	$176.30	$176.30
Purchase #2	$127.33	12.476%	$143.2157	$143.22	$143.20	$143.20
Purchase #3	$152.79	12.321%	$171.6153	$171.62	$171.60	$171.60
Purchase #4	$61.85	13.588%	$70.2542	$70.25	$70.25	$70.30
Purchase #5	$214.84	3.508%	$222.3766	$222.38	$222.40	$222.40
Purchase #6	$42.46	6.575%	$45.2517	$45.25	$45.25	$45.30
Purchase #7	$247.35	11.308%	$275.3203	$275.32	$275.30	$275.30
7 purchase totals =	$1,012.19		$1,104.3377	$1,104.34	$1,104.30	$1,104.40